The present invention relates to friction clutches in general, and more particularly to improvements in friction clutches which are especially suited for use in motor vehichles. Still more particularly, the invention relates to improvements in friction clutches of the type wherein a clutch cover is provided with two concentric annular seats flanking an intermediate portion of a diaphragm spring whose outer marginal portion can bear upon a pressure plate and whose radially inwardly extending prongs can be acted upon to engage or disengage the clutch.
It is already known to provide the diaphragm spring of a friction clutch with substantially radially extending reinforcing portions which are formed into or otherwise applied to the prongs, which extend from one side of the spring and which serve to stiffen the prongs in the regions where their outer end portions merge into the aforementioned outer marginal portion of the spring. It is also known to provide that seat which is adjacent to the one side of the diaphragm spring with arcuate portions which bridge the reinforcing portions of the spring. In many instances, each of the seats constitutes a wire ring and each of these rings is affixed to the cover of the friction clutch, e.g., by means of rivets which extend through the enlarged outer end portions of slots between some or all of the prongs. The arcuate portions are normally provided in that seat which is more distant from the cover so that the other seat can be made integral with the cover. It is also possible to provide the cover with a circumferentially complete or interrupted rib which constitutes one of the two seats for the diaphragm spring. Furthermore, the arcuate portions can be provided in the integral rib-shaped portion of the seat so that the other seat can constitute a simple wire ring.
The provision of reinforcing portions on some or all of the prongs reduces the area of contact between the spring and that seat which is formed with arcuate portions because the arcuate portions are normally out of contact with the adjoining reinforcing portions. This entails a pronounced increase in the magnitude of forces acting between the diaphragm spring and that seat which is formed with the arcuate portions per unit area of contact between these parts. The just mentioned forces are especially pronounced in the regions of enlarged outer end portions of slots between the prongs of the diaphragm spring. The situation is aggravated due to the fact that the just mentioned regions are already subjected to very pronounced stresses. Therefore, the configuration of the outer end portions of the slots must be selected with great care in order to avoid an excessive increase of forces and resulting damage to or total destruction of the diaphragm spring. This often necessitates replacement of the entire clutch, especially if the diaphragm spring is more or less permanently installed between the two seats which, in turn, are permanently or more or less permanently installed on or made part of the cover of the friction clutch.